The main intent of the Core is to foster multi-disciplinary interactions for further advances in AIDS research to bridge basic and clinical investigations in the area of HIV-related pathogenesis, treatment strategies and, importantly, vaccine development. Specific aims: 1) Acquire mucosal biopsies for RNA/DNA extraction and serial sectioning (OCT-embedded samples for frozen sections and paraffin-embedded samples) of HIV-seropositive subjects and seronegative controls with corresponding peripheral blood samples (these are sampled in conjunction with the Virology Core). 2) Provide mononuclear suspensions of gastrointestinal mucosal samples from seropositive subjects and seronegative controls utilizing recently optimized isolation techniques. Phenotypic characterization of lymphocyte subsets will be determined with the assistance of the Flow Cytometry Core. 3) Consult in the clinical aspects of study design relating to mucosal HIV projects including: patient selection and tissue procurement, sample processing, assistance in institutional review board submissions, hypothesis testing, detecting changes in the local versus systemic immune response, evaluating treatment responses at the tissue level, etc. 4) Assist in obtaining additional clinical and tissue material for studies by (a) direct recruitment of community patients sources including women and minorities, (b) recruitment of clinicians with access to other mucosal sites (in conjunction with the Clinical Core) and (c) utilization of an IRB-approved Core consent form for pilot studies. 5) Develop and standardize new techniques as needed such as lymphocyte isolation from other mucosal sites, mucosal immunoglobulin collection, quantification of mucosal cytokine mRNA, mucosal ELISpot (often in collaboration with other Cores).